Once turned on, it calibrates to its environment and then detects an object approaching (well, let's face it, a cat, this is about cats). At a certain threshold it starts the mad barking.

The project is based on original brilliant work by LuckyResistor. Boldport collaborated on the project, although the highly optimised MCU code—every bit is sacred, every bit is great—is solely the work of LuckyResistor.